Reevaluating the mechanisms of focal ictogenesis: The role of low‐voltage fast activity

The mechanisms that control the transition into a focal seizure are still uncertain. The introduction of presurgical intracranial recordings to localize the epileptogenic zone in patients with drug‐resistant focal epilepsies opened a new window to the interpretation of seizure generation (ictogenesis). One of the most frequent focal patterns observed with intracranial electrodes at seizure onset is characterized by low‐voltage fast activity in the beta‐gamma range that may or may not be preceded by changes of ongoing interictal activities. In the present commentary, the mechanisms of generation of focal seizures are reconsidered, focusing on low‐voltage fast activity patterns. Experimental findings on models of temporal lobe seizures support the view that the low‐voltage fast activity observed at seizure onset is associated with reinforcement and synchronization of inhibitory networks. A minor role for the initiation of the ictal pattern is played by principal neurons that are progressively recruited with a delay, when inhibition declines and synchronous high‐voltage discharges ensue. The transition from inhibition into excitatory recruitment is probably mediated by local increase in potassium concentration associated with synchronized interneuronal firing. These findings challenge the classical theory that proposes an increment of excitation and/or a reduction of inhibition as a cause for the transition to seizure in focal epilepsies. A new definition of ictogenesis mechanisms, as herewith hypothesized, might possibly help to develop new therapeutic strategies for focal epilepsies.     

First record of species Dicranotaenia synsacculata Macko, 1988 (Cestoda, Hymenolepididae) of the goldeneye Bucephala clangula (Linneus, 1758) in Poland

During parasitological studies of 32 specimens of the goldeneye Bucephala clangula L., twenty seven cestode specimens were found. Four of them, isolated from the jejunum of two young female hosts, were determinated as Dicranotaenia synsacculata Macko, 1988. We based on the shape of cirrus fused with sacculus accessorius internus, shape and size of scolex and other organs. This is the first record of this species in Poland.     

Topographic distribution of direct and hippocampus- mediated entorhinal cortex activity evoked by olfactory tract stimulation

Olfactory information is central for memory-related functions, such as recognition and spatial orientation. To understand the role of olfaction in learning and memory, the distribution and propagation of olfactory tract-driven activity in the parahippocampal region needs to be characterized. We recently demonstrated that repetitive stimulation of the olfactory tract in the isolated guinea pig brain preparation induces an early direct activation of the rostrolateral entorhinal region followed by a delayed response in the medial entorhinal cortex (EC), preceded by the interposed activation of the hippocampus. In the present study we performed a detailed topographic analysis of both the early and the delayed entorhinal responses induced by patterned stimulation of the lateral olfactory tract in the isolated guinea pig brain. Bi-dimensional maps of EC activity recorded at 128 recording sites with 4 x 4 matrix electrodes (410 microm interlead separation) sequentially placed in eight different positions, showed (i) an early (onset at 16.09 +/- 1.2 ms) low amplitude potential mediated by the monosynaptic LOT input, followed by (ii) an associative potential in the rostral EC which originates from the piriform cortex (onset at 33.2 +/- 2.3 ms), and (iii) a delayed potential dependent on the previous activation of the hippocampus. The sharp component of the delayed response had an onset latency between 52 and 63 ms and was followed by a slow wave. Laminar profile analysis demonstrated that in the caudomedial EC the delayed response was associated with two distinct current sinks located in deep and in superficial layers, whereas in the rostrolateral EC a small-amplitude sink could be detected in the superficial layers exclusively. The present report demonstrates that the output generated by the hippocampal activation is unevenly distributed across different EC subregions and indicates that exclusively the medial and caudal divisions receive a deep-layer input from the hippocampus. In the rostrolateral EC, specific network interactions may be generated by the convergence of the direct olfactory input and the olfaction-driven hippocampal output.     

Casting Welding from Magnesium Alloy Using Filler Materials That Contain Scandium

Based on the results achieved in systematic studies of structure formation and the formation of multicomponent phases, a scandium-containing filler metal from system alloy Mg-Zr-Nd for welding of aircraft casting was developed. The influence of scandium in magnesium filler alloy on its mechanical and special properties, such as long-term strength at elevated temperatures, was studied by the authors. It is established that modification of the magnesium alloy with scandium in an amount between 0.05 and 0.07% allows a fine-grained structure to be obtained, which increases its plasticity up to 70% and heat resistance up to 1.8 times due to the formation of complex intermetallic phases and the microalloying of the solid solution. Welding of the aircraft castings made of magnesium alloy with scandium-containing filler material allows obtaining a weld with a dense homogeneous fusion zone and the surrounding area without any defects. The developed filler material for welding surface defects (cracks, chips, etc.) formed during operation on aircraft engine bodies makes it possible to restore cast body parts and reuse them. The proposed filler material composition with an improved set of properties for the welding of body castings from Mg-Zr-Nd system alloy for aircraft engines makes it possible to increase their reliability and durability in general, extend the service life of aircraft engines, and obtain a significant economic effect.     

From the Cover: Benthic invaders control the phosphorus cycle in the world’s largest freshwater ecosystem

The productivity of aquatic ecosystems depends on the supply of limiting nutrients. The invasion of the Laurentian Great Lakes, the world’s largest freshwater ecosystem, by dreissenid (zebra and quagga) mussels has dramatically altered the ecology of these lakes. A key open question is how dreissenids affect the cycling of phosphorus (P), the nutrient that limits productivity in the Great Lakes. We show that a single species, the quagga mussel, is now the primary regulator of P cycling in the lower four Great Lakes. By virtue of their enormous biomass, quagga mussels sequester large quantities of P in their tissues and dramatically intensify benthic P exchanges. Mass balance analysis reveals a previously unrecognized sensitivity of the Great Lakes ecosystem, where P availability is now regulated by the dynamics of mussel populations while the role of the external inputs of phosphorus is suppressed. Our results show that a single invasive species can have dramatic consequences for geochemical cycles even in the world’s largest aquatic ecosystems. The ongoing spread of dreissenids across a multitude of lakes in North America and Europe is likely to affect carbon and nutrient cycling in these systems for many decades, with important implications for water quality management.

Invasive species are well known to impact many aspects of ecosystems, including biodiversity, food web structure, and ecosystem functioning (1). The Laurentian Great Lakes, the largest freshwater ecosystem on Earth, serve as a dramatic example of large-scale reorganization of geochemical cycles by an invader. Following the establishment of zebra and quagga (dreissenid) mussels in littoral areas of the Great Lakes in the late 1980s, nutrients and productivity were redirected to the nearshore (2), while pelagic primary productivity declined by as much as 70% (3–7). Having outcompeted zebra mussels, quagga mussels now are abundant in most of the bottom areas in all of the Great Lakes except Lake Superior, often at densities exceeding 10,000 individuals per square meter (8–11). The expansion of quagga mussels coincided with unexplained changes in the abundances and distributions of other benthos (12) and modifications to the structure and phenology of the phytoplankton community (13) and food web structure (14, 15). Less attention was given to observations that pelagic concentrations of phosphorus (P), the productivity-limiting nutrient in the Great Lakes, decreased even while external P inputs remained steady (16, 17). The dynamics of P have practical importance because regulation of P inputs from the watershed has been the primary tool for managing water quality in the Great Lakes. In particular, reductions in P loadings are credited for the recovery from eutrophic conditions of the 1970s, and a further 40% reduction has been proposed recently to curtail recurring algal blooms in Lake Erie (18).However, will the dreissenid-colonized lakes respond to further reductions in P input in the same way they did in the past? The unprecedented changes in the Great Lakes induced by dreissenids warrant a reevaluation of P cycling and budgets, which need to account for mussel biomass and modified benthic–pelagic exchanges. The problem extends well beyond the Great Lakes: dreissenids have now been documented in thousands of inland lakes and rivers in North America (19) and Europe (20, 21) and may affect freshwater nutrient dynamics on continental scales.The dynamics of P concentrations in lake water are regulated by the balance of P sources and sinks. These include inputs from the watershed, removal with outflow, and net burial in sediments (16, 22). The role of the benthic system is significant. Sediments can recycle a large fraction of the deposited P and resupply it to the water column. Before the dreissenid invasion, this recycled fraction of P sedimentation varied from as little as 10% in Lake Michigan to as much as 60% in Lake Erie (16), contributing 15 to 48% of all (internal and external) phosphorus inputs to the water column (16). The efficiency of sedimentary P recycling also determines the inertia with which P concentrations in the water column respond to external inputs (16). When only a small fraction of the deposited P is recycled, total phosphorus (TP) concentrations respond with time lags of only a few years, even in large lakes (16). Recent TP dynamics in the Great Lakes, however, seems to have been decoupled from external P loadings (17), with change beginning shortly after the dreissenid invasion.Aquatic consumers can strongly impact the cycling of nutrients (23–26). High abundances of dreissenid mussels in particular can modify the sediment–water exchanges of phosphorus. As epibenthic filter feeders, dreissenids continually remove particulate P from bottom water (27). Most (∼90%) of the ingested phosphorus is remobilized (28): apart from a small portion incorporated into soft tissue and shell, P is either excreted into the water column in dissolved form or egested onto the sediment surface as feces and pseudofeces (27, 29, 30). The egested P is quickly remineralized to dissolved P via microbial decomposition (31). Mussel biomass P becomes mobilized over longer time scales through decomposition of dead tissues, release of gametes, and dissolution of shells (32). All of these processes modify the natural exchanges of P between sediments and water column, potentially affecting whole-system P mass balance. However, the effects of dreissenids on the sedimentary P fluxes have been evaluated in the Great Lakes only locally (27, 29, 30), and possibilities of regime-changing tipping points (33) or hysteresis in the geochemical dynamics have not been explored.Here, we show that the increase of invasive mussel biomass and consequent enhancement of benthic P fluxes have pushed the Great Lakes into a new dynamic regime where P concentrations and fluxes are controlled by mussel physiology and population dynamics, while responses to external phosphorus inputs have become muted. This regime is sensitive to biological perturbations, responds more slowly to external regulation, and presents unique challenges to managing these large ecosystems.     

Quantitative estimation of information influence of law intensive laser radiation on macro- and the microelement status in patients of the senior age groups

Law intensive laser radiation is a multifactorial, inherently information-power influence on biological tissues. Coinciding under characteristics with natural, the dosed out external influence is necessary for live organisms not only as a source of free energy, but also as the supplier of building materials. As an alarm indicator we had chosen the change of concentration of microcells in blood whey, owing to high sensitivity of this parameter. Photoexcitation conducts to acceleration of chemical reactions, in particular the oxidation-reduction. The probability of "capture" of a photon by a molecule depends on its energy and from power level of a molecule. Absorption of a photon by a molecule occurs when the direction transition coincides with fluctuations of an electric vector of a light wave. Efficiency of carrying over can be defined on time of a life of a luminescence. The quantum exit can be expressed through the relation of intensity of fluorescence to a difference of capacities of falling and leaving light streams. As a result of occurrence of a gradient of temperature in around membrane areas there is a change of electric potential of a membrane that causes outflow of ions from a membrane. Thereof the albuminous channels causing active transportation of ions and polar molecules reveal. As a result of change of electrochemical ionic balance lability of microcells to information doses of laser influence is provided.     

Distribution of the olfactory fiber input into the olfactory tubercle of the in vitro isolated guinea pig brain

The olfactory tubercle (OT) is a cortical component of the olfactory system involved in reward mechanisms of drug abuse. This region covers an extensive part of the rostral ventral cerebrum and is relatively poorly studied. The intrinsic network interactions evoked by olfactory input are analyzed in the OT of the in vitro isolated guinea pig brain by means of field potential analysis and optical imaging of voltage-sensitive signals. Stimulation of the lateral olfactory tract induces a monosynaptic response that progressively decreases in amplitude from lateral to medial. The monosynaptic input induces a disynaptic response that is proportionally larger in the medial portion of the OT. Direct stimulation of the piriform cortex and subsequent lesion of this pathway showed the existence of an associative disynaptic projection from the anterior part of the piriform cortex to the lateral part of the OT that integrates with the component mediated by the local intra-OT collaterals. Optical and electrophysiological recordings of the signals evoked by stimulation of the olfactory tract during arterial perfusion with the voltage-sensitive dye di-2-ANEPEQ confirmed the pattern of distribution of the mono and disynaptic responses in the OT. Finally, current source density analysis of laminar profiles recorded with 16-channel silicon probes confirmed that the monosynaptic and disynaptic potentials localize in the most superficial and the deep portions of the plexiform layer I, as suggested by previous reports. This study sets the standard for further analysis of the modulation of network properties in this largely unexplored brain region.     

Cellular correlates of spontaneous periodic events in the medial entorhinal cortex of the in vitro isolated guinea pig brain

Periodic potentials characterized by fast oscillations superimposed on a slow complex event are typically observed in cortical structures during sleep and anaesthesia. In the entorhinal cortex (EC) similar spontaneous periodic events (SPEs) have been described both in vivo and in vitro. Simultaneous extracellular and intracellular recordings from superficial neurons of the entorhinal cortex of the isolated Hartley guinea pig brain preparation demonstrated that SPEs recur with a periodicity of 2-10 s and correlate to neuronal firing superimposed on a depolarizing plateau that lasts 0.7-1 s. During SPEs, putative interneurons in all layers discharged high frequency firing (> 100 Hz), whereas no activity was observed in principal neurons of deep entorhinal cortex layers. Linear correlation analysis demonstrated a tight relationship between the fast component of the extracellular SPE and subthreshold oscillatory activity/neuronal firing in both superficial neurons and putative interneurons; firing of deep principal cells was independent from SPEs occurrence. The present study demonstrates that recurrent spontaneous events analogous to periodic activity observed during sleep/anaesthesia are generated in the entorhinal cortex by the interactions between superficial neurons and interneurons.     

Downregulation of putative tumor suppressor gene TSC-22 in human brain tumors

BACKGROUND AND OBJECTIVES: Our objective was to identify differentially expressed genes involved in the pathogenesis of glioblastoma multiforme (GBM). METHODS: Screening of arrayed human fetal brain and human postnatal brain cDNA libraries was performed by differential hybridization with glioblastoma multiforme and human normal brain cDNAs. RESULTS: Repeated differential hybridization of more than 100 cDNA clones selected by primary screening and analysis of RNA from adult normal brain and glial tumors showed 16 nucleotide sequences differentially expressed between normal brain and brain tumors. Among others, decreased content in astrocytic tumors was determined for TSC-22 mRNA corresponding to cDNA in the ICRFp507J1041 clone from human fetal brain cDNA library. Northern blot hybridization of RNA from different human brain tumors showed very low amounts of TSC-22 mRNA in most investigated samples of GBM, anaplastic astrocytoma, and some other tumors. Complete lack of expression of TSC-22 occurred in one sample of anaplastic astrocytoma, as well as in meningioma, brain sarcoma, sarcomatous meningioma, and oligodendroglioma. The differential expression of TSC-22 gene was confirmed by semiquantitative RT-PCR in 15 samples of astrocytomas WHO grade II-IV and three samples of normal brain. CONCLUSIONS: Significantly decreased levels of TSC-22 mRNA in human brain and salivary gland tumors and antiproliferative role of TSC-22 strongly suggest a tumor suppressor role for TSC-22. J.